Oneirodidae

Dreamers

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Introduction

The Oneirodidae is by far the largest, most complex, and certainly the least understood family of the suborder. With 16 genera and 62 species, it contains nearly 40% of all recognized ceratioids. Of the 16 genera, five are currently represented by only one, two, or three adolescent or adult females; only eight are represented by more than a dozen females. Males have been described for only seven genera, while larvae are known for only eight. But despite the rareness of most recognized taxa, new oneirodids are continually being described.

Although not characteristic of all members of the family, the following additional features are important in differentiating the Oneirodidae: each frontal with a prominent ventromedial extension (absent in Lophodolos); sphenotic spines usually present (absent in Chaenophryne); pterosphenoid usually present (absent in Lophodolos); hyomandibular usually with a double head (single head in Bertella); opercle bifurcate, dorsal fork supported by a single rib (except in larval females of Danaphryne); anterior subopercular spine usually absent (blunt projection present in most specimens of Chaenophryne, adolescent females of Lophodolos, and some larvae and males of Dolopichthys and Pentherichthys); quadrate and articular spines usually well developed (small to rudimentary in Chaenophryne); lower jaw usually with a well-developed symphysial spine (small, blunt to absent in Chaenophryne, absent in Pentherichthys); pharyngobranchial I usually absent (present in Spiniphryne and Oneirodes); pharyngobranchial II usually well developed and heavily toothed (reduced and toothless in Bertella, Microlophichthys, and some species of Oneirodes; absent in Pentherichthys and Lophodolos); epibranchial teeth usually absent (present on epibranchial I of some species of Oneirodes); ossified posteroventral process of coracoid usually absent (present in Spiniphryne and Oneirodes); pelvic bone usually rod-like, with or without slightly expanded distal tip (triradiate or broadly expanded distally in Chaenophryne; Pietsch, 1975:79, fig. 2); dermal spinules usually absent (well developed in Spiniphryne, minute and widely scattered in Oneirodes).

Metamorphosed males are distinguished from those of all other ceratioid families in having the following combination of character states: eyes directed laterally, elliptical in shape, axis short, diameter of pupil greater than that of lens; olfactory organs large, anterior nostrils situated close together and opening forwards; posterior nostrils lateral, usually larger than eye; nasal area usually pigmented, sometimes slightly inflated; jaw teeth absent; dermal spinules of snout absent; posterior end of upper denticular remote from anterior end of pterygiophore of illicium; fin-ray counts as given for metamorphosed females; skin naked (but males of the spiny-skinned oneirodid genus Spiniphryne are unknown); free-living, non-parasitic, with two exceptions, both apparently facultative couplings: a single known attached pair of Leptacanthichthys gracilispinis and another of Bertella idiomorpha (see Pietsch, 2005).

There is no satisfactory combination of features that serve to adequately diagnose oneirodid larvae. As stated by Bertelsen (1951:71), it is “easier in practice to make the identification [of larvae] from the features characteristic of each of the many genera within the family.” To a somewhat lesser extent, the same could also be said for the metamorphosed males and females.

Description

Metamorphosed females highly variable, ranging from short and deep-bodied, more-or-less globular (e.g., Oneirodes and Chaenophryne), to elongate and fusiform (e.g., Dolopichthys and Leptacanthichthys); head usually short, approximately 35% SL or less (30% SL in Dermatias, nearly 50% SL in some species of Chaenophryne); mouth large, opening horizontal to nearly vertical, cleft extending well past eye in most genera (terminating anterior to eye in Spiniphryne, Danaphryne, Phyllorhinichthys, Puck, Ctenochirichthys, and Bertella); jaw teeth slender, recurved, and depressible, those in upper jaw usually somewhat shorter and fewer than those in lower jaw (upper-jaw teeth more numerous than lower in Danaphryne, Microlophichthys, Tyrannophryne, Phyllorhinichthys, Puck, Leptacanthichthys, and Ctenochirichthys); number of premaxillary and dentary teeth highly variable, lower jaw with fewer than 20 (e.g., Phyllorhinichthys and some species of Oneirodes) to nearly 600 (e.g., some species of Dolopichthys); vomerine teeth usually present (lost with growth in Bertella and some species of Dolopichthys, absent in Lophodolos and Pentherichthys); epibranchial I free from wall of pharynx; epibranchials I-IV closely bound together; proximal one-fourth to one-half of ceratobranchial I bound to wall of pharynx, distal three-fourths to one-half free; epibranchial IV and ceratobranchial IV bound to wall of pharynx, no opening behind fourth arch; gill filaments present on proximal tips of epibranchials II-IV, on proximal tip of ceratobranchial I, and full length of ceratobranchials II-IV; pseudobranch absent; length of illicium highly variable, extremely short and nearly fully enveloped by tissue of esca (e.g., Tyrannophryne) to 75% SL (e.g., some species of Oneirodes and Dolopichthys); anteriormost tip of pterygiophore of illicium usually exposed (hidden in Tyrannophryne), emerging at tip of snout from between eyes or more posteriorly; posterior end of pterygiophore usually concealed under skin (protruding on dorsal surface of trunk behind head in Oneirodes); escal bulb simple to highly complex; neuromasts of acoustico-lateralis system located at tips of low rounded cutaneous papillae, pattern of placement as described for other ceratioids (Pietsch, 1969, 1972, 1974a, 1974b).

The largest known female is a 370-mm specimen of Oneirodes heteronema, collected by the Walther Herwig during the 1982 expedition to the mid-Atlantic Ridge. The largest known male measures 16.5 mm.

Distribution

The Oneirodidae is widely distributed throughout the more productive waters of all three major oceans of the world. Unlike some ceratioid families (e.g., Melanocetidae), which appear to be limited by the Arctic and Antarctic Polar Fronts, oneirodids extend northward to at least 66º in the North Atlantic and 62º in the Bering Sea, and southward into the Southern Ocean to at least 65ºS. It is represented in the Caribbean Sea and in the gulfs of Aden, California, and Mexico; but, like all other ceratioids, it has not been collected in the Mediterranean Sea.

Key to Males and Females of Genera of the Oneirodidae

Females

Because several genera are known from very few specimens (only two adolescent females in Tyrannophryne, Chirophryne, and Puck), and for many, larvae and males are unknown, the following keys to females and males, both modified from Bertelsen (1951:74-76) and Pietsch (1974a:30), are tentative and may not include the best diagnostic characters.

13A. Length of quadrate spine greater than length of articular spine; dorsal profile of frontal bones convex; esca with more than a single appendage, either five separate appendages arising from dorsal surface or three dorsal appendages and a lateral filament; anal-fin rays 4 (go to 14)

14B. Length of anterior maxillomandibular ligament less than one-half length of premaxilla, gape of mouth not extending beyond eye; subopercle long and narrow, upper end tapering to a point; esca with a lateral filament (Puck Pietsch, 1978)

15A. Hyomandibula with a single head (Bertella Pietsch, 1973)

15B. Hyomandibula with a double head (Dolopichthys Garman, 1899)

Males

In the following key, slightly modified from Bertelsen (1951:75), it is uncertain how much diagnostic value can be ascribed to the number of denticular teeth and olfactory lamellae; these presumably increase during adolescent development and therefore may be subject to greater individual variation than indicated here.

Other Names for Oneirodidae

References

Garman, S. 1899. Reports on an exploration off the west coasts of Mexico, Central and South America, and off the Galapagos Islands, in charge of Alexander Agassiz, by the U. S. Fish Commission steamer "Albatross," during 1891, Lieut. Commander Z. L. Tanner, U. S.N., commanding. XXVI. The fishes. Mem. Mus. Comp. Zool., 24, 431 pp.

Lloyd, R. E. 1909. A description of the deep-sea fish caught by the R. I. M. S. Ship "Investigator" since the year 1900, with supposed evidence of mutation in Malthopsis. Mem. Indian Mus., Calcutta, 2(3): 139-180.

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Oneirodidae. Dreamers.
Authored by
Theodore W. Pietsch.
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